Fluid operated reciprocating motor

ABSTRACT

A fluid operated reciprocating motor for use particularly in driving earth tampers includes a case, a piston mounted for reciprocation in the case, and an actuating hydraulic circuit driving the piston. The circuit includes high and low pressure conduits interconnecting the piston faces with a source of high pressure fluid and a low pressure exhaust line. It also includes a pressure actuatable valve in series in the conduits. The valve includes a valving element shiftable by the application of fluid pressure between first and second positions wherein it directs the flow of high pressure fluid alternately against the respective piston faces. Fluid valve control circuits are present at each end of the piston and are arranged for applying fluid pressure to the valving element at the completion of each piston stroke, for shifting the valving element to a position in which it reverses the piston stroke direction. Damping means are associated with the piston for damping its movement at the end of each stroke preliminary to reversal of the stroke direction.

United States Patent Ackley Apr. 2, 1974 FLUID OPERATED RECIPROCATING MOTOR Primary Examiner-Paul E. Maslousky [75] Inventor: Edward L. Ackley, Portland, Greg.

A A M M f C [57] ABSTRACT [73] Sslgnee' z z ig ompany A fluid operated reciprocating motor for use particularly in driving earth tampers includes a case, a piston [22] Filed: Aug. 18, 1972 mounted for reciprocation in the case, and an actuating hydraulic circuit driving the piston. The circuit in- [21] App! N 28l748 cludes high and low pressure conduits interconnecting the piston faces with a source of high pressure fluid Cl /297, and a low pressure exhaust line. It also includes a pres- 92/ 92/143 sure actuatable valve in series in the conduits. The

Folb Folb 1 valve includes a valving element shiftable by the appli- [58] Field of Search 91/300, 335, 394, 446, cation of fluid pressure between first and second posi- 91/297, 1; 92/85, 143 tions wherein it directs the flow of high pressure fluid alternately against the respective piston faces. Fluid [56] References Cited valve control circuits are present at each end of the UNITED STATES PATENTS piston and are arranged for applying fluid pressure to 858 397 7/1907 Johnson 91,300 the valving element at the completion of each piston 15741762 M1926 i, 91,300 stroke, for shifting the valving element to a position in 2,955,573 10/1960 Feucht 0. 92/85 which it reverses the Piston Stroke direction Damping 3,113,432 12/1963 Watson 91/446 means are associated with the piston for damping its 3,322,038 5/1967 Dobson 91/300 movement at the end of each stroke preliminary to re- 3,329,Q68 7/1967 Klaus 92/85 versal f the troke directiQfL 3,376,791 4/1968 Ashfield et al... 9l/394 3,496,835 2/1970 Siegmann 91 300 16 Clalms, l4 Drawmg Figures l l l l 1 1 1 1 I -l I I 1 A l 1/ [4 112 781: eoa

PATENTED APR 2 I974 SHED 1 (If 5 NOT MTENTEI] APR 2 I974 ME? 3 BF 5 pow wwow

PATENTEDAPR 2 i974 SHEET t (If 5 @3 0Q @9 VS PATENTEU APR 2 1974 SHEET 5 BF 5 mm dww 1 FLUID OPERATED RECIPROCATING MOTOR RELATED APPLICATION BACKGROUND OF THE INVENTION This invention relates to fluid operated reciprocating motors. Although the motors may comprise air motors, the inventionpertains particularly to hydraulically operated motors of the class useful in driving mechanisms such as earth tampers, shaking screens, vibrators for dump truck bodies, reciprocating jack hammers, scalers, breakers, and shovels. it is described herein with particular reference to hydraulic earth tampers, although no limitation thereby is intended.

Earth tampers of the class employed for tamping earth around the bases of newly installed telephone poles, etc., are technically inadequate for several reasons. Their operating speeds are either too slow, or are restricted to a limited range. lnorder to obtain adequate operating speeds, the construction of the tamper is made so light that mechanical failures occur during use. The action of the control valve is not sufficiently positive and may result in arresting the motion of the tamper piston in an intermediate position from which itcannot be started without shaking or disassembling the' tamper. Provision is'not made for damping the stroke of the piston simultaneously with its reversal,

thereby slamming together moving parts with consequent potential damage to both tamper and operator. The driving mechanisms are not adaptable to lending versatility in contour and size to the tampers as required tomake them suitable for varied applications.

It is the object of the present invention to provide a fluid operated'r eciprocating motor, specifically an hydraulically operated reciprocating motor for use in driving an earth tamper, which may be operated smoothly over a wide range of Operating speeds; which is-su'bj ecttoiprecise throttle control; which is of rugged construction; which is trouble free in operation and easy to'maintain; which has a damped piston motion; and which is readily adaptable for inclusion in tampers and other apparatus of varied contour and size.

SUMMARY OF THE INVENTION It has now been found that the foregoing and related objects can be readily attained in a fluid operated reciprocating motor which comprises a case, a piston having front and back faces'and which is mounted for reciprocating in the case, and a hydraulic circuit arranged for driving a piston in reciprocating motion.

.fluid pressure between first and second positions wherein it directs the flow of high pressure fluid alternately against the front and back faces. A piston actuated pressure altering means is arranged for applying fluid pressure to a selected area of the valving element at the completion of each piston stroke This shifts the valving element to a position in which it reverses the piston stroke direction. Damping means are associated with the piston for damping its movement preliminary to each stroke reversal.

In accordance with the illustrated embodiment of the invention, the damping means comprises check valve means including a guide sleeve which slidably receives the piston therein. The guide sleeve cooperates with the piston to provide at least one chamber between the guide sleeve and the piston. Means interconnect the chamber in fluid flow relation with the low pressure exhaust line for periodically providing a flow of fluid from the low pressure exhaust line to the chamber. The guide sleeve has an annular groove formed therein and also has a plurality of openings of predetermined size formed therethrough interconnecting the annular groove with the chamber. The check valve means further includes a seal ring seated in the. annular groove. The seal ring expands in response to fluid pressure being applied thereto as the piston approaches the termination of a recoprocation to permit a controlled flow of fluid from the chamber through the plurality of openings to the annular groove thereby to cause a damping of the movement of the piston. I

The hydraulic circuit in accord with the illustrated embodiment of the invention includes a valve housing defining a valve chamber, a spool valve, pressure equalizing conduit means, and valve shifting conduit means. The pressure equalizing conduit means interconnects the high pressure conduit means in fluid flow relationship with each end of the valve chamber such as to normally equalize the fluid pressure applied in the valve chamber against the ends of the spool valve. The valve shifting conduit means includes a first conduit means operable for interconnecting one end of the valve chamber with the low pressure exhaust line during at least a portion of the movement of the piston from its first position to its second position such as to permit a flow if. fluid from the aforesaid one end of the valve chamber to the low pressure exhaust line thereby to establish a pressure differential across the ends of the spool valve to cause the spool valve to shift from its first to its second position as the piston completes its movement from its first to its second position. The valve shifting conduit means also includes a second conduit means operable for interconnecting the other end of the valve chamber with the low pressure exhaust line during at least a portion of the movement of the piston from its second position to its first position such as to permit a flow of fluid from the aforesaid other end of the valve chamber to the low pressure exhaust line thereby to establish a pressure differential across the ends of the spool valve to cause the spool valve to'shift from its second to its first position.

In accord with the illustrated embodiment of, the invention, the piston includes a cylindrical bore extending inwardly from the rear end of the piston. The back face of the piston comprises the end wall of the cylindrical bore. The cylindrical bore in the piston has a chamber substantially less than the overall diameter of the piston such hat only a relatively small amount of fluid is required to fill the cylindrical bore to apply pressure against the back face to cause movement of the piston. In addition, the back face of the piston has a substantially greater area than the front face of the piston such that in the event the movement of the piston is interrupted at a point other than the termination of a reciprocation the differential pressure of the fluid applied across the back face and the front face operates to cause the piston to move to its second position. Finally, the fluid operated reciprocating motor further comprises in accord with the preferred embodiment of the invention a resilient abutment means mounted in the case forward of the second position of the piston. The resilient abutment means includes metallic conduit means arranged for engagement by the piston in the event of a malfunction in the hydraulic circuit to cause the emision of a metallic sound from the engagement of the metallic contact means by the piston thereby to provide an audible indication of the occurrence of the malfunction.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a view in elevation of a tamper incorporating the herein described fluid operated reciprocating motor; I

FIG. 2 is an exploded perspective view of the motor;

FIGS. 3a and 3b are complementary fragmentary views of the motor in longitudinal section, taken along line 3-3 of FIG. 1;

FIGS. 4, 5, 6 and 7 are sectional views taken along lines 4-4, 55, 66 and 7-7, respectively, of FIG. 3b;

FIG. 8 is a fragmentary, longitudinal sectional-view similar to FIG. 3b but illustrating the control valve in its reverse setting;

FIG. 9 is a view in elevation, partly broken away, of a channeled sleeve which is a component of the motor;

FIG. 10 is a schematic fluid circuit for the motor;

FIG. 11 is a schematic fluid circuit for the motor illustrating the fluid circuitry for reversing the direction of movement of the piston at the end of its movement in one direction;

FIG. 12 is a schematic fluid circuit for the motor similar to FIG. 11 illustrating the fluid circuitry for reversing the direction of movement of the piston at the end of its movement in the other direction; and

FIG. 13 is a schematic fluid circuit for the motor illustrating the fluid circuitry forfdamping the movement of the piston at the end of each reciprocation thereof.

I DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENT An earth tamper including the herein described fluid operated reciprocating motor is illustrated in FIG. 1. The tamper includes a fluid operated motor 12, herein described as an hydraluic motor, a handle 14, a hose 16 which cases the tubes connecting the motor with a source of hydraulic fluid, and a tamping foot 18. These various elements may be contoured and dimensioned as required for various applications.

For example, the apparatus may be of substantial size with a long stroke as required for tamping earth in a 6 foot hole surrounding a telephone pole, or it may be of reduced size for less substantial applications. Also, foot 18 may assume a contour tailored to the intended application: e.g. arcuate, where it is designed to tamp around the base of a round pole.

The individual elements making up the motor-.12 are illustrated in disassembled condition in FIG. 2.

In addition to handle 14, the exterior members comprise an elongated piston case 20 which may comprise a section of pipe of suitable length; a nose piece 22 threaded into the outer end of case 20 and having therethrough a longitudinal bore 23; and a valve case 24 having therethrough a longitudinal bore 26 communicating with a transverse bore 28. Case 24 is secured to the inner end of case 20- by suitable means, as by being threaded thereto.

A piston indicated generally at 30 is seated for reciprocating movement within case 20 and nose piece 22.

The piston has a forwardly extending piston rod 32 which is received in sliding relation in nose piece 22. Wiper 34, and dirt trap 36 adjacent the outer end of the nose piece 22, as seen in FIG. 3a, protect the inner mechanism from outside contamination.

An enlarged section of bore 23 of nose piece 22 contains a packing which may be variously constiuted, but which, in the illustrated form of the invention, comprises a rubber or plastic main shaft seal 40, a metal washer 42, a loosely fitted O-ring 44, and a metal bumper ring 46.

The above packing assembly serves three functions. First it prevents the escape of fluid. Secondly, it lubricates the piston rod. Third, although it is not intended that the piston 30 should contact metal ring 46 of the packing in the normal operation of the tamper, contact is made in the event of malfunction. The resulting metal to metal contact causes the emission of a metallic sound which warns the operator to shut off the tool before damage to its component parts can occur.

Piston 30 further is provided with a forward piston face 48, 48a and a rearward piston face 50. It is to be noted wiht reference to FIG. 3a that piston face 50 is provided as the end wall of a cylindrical bore 52 extending inwardly from the rear end of the piston 30. The diameter of this bore 52 is relatively small, as compared to the overall diameter of the piston 30. This makes possible high speed reciprocation of a large, strong piston since even though the piston 30 is of large diameter only a relatively small chamber need be filled with hydraulic fluid in order to advance the piston 30 fully to its extended position.

It is to be noted further that the area of back face 50, which produces the power stroke, is substantially greater than the area of front face 48, 48a which is merely sufficient to return the piston 30 to its starting position. This not only provides the necessary power, but also insures that, because of the differential pressure applied to the two faces 48, 48a and '50, respectively, the piston 30 will move to a terminal, operative position in the event that the valve controlling the power fluid becomes stuck in an intermediate position, or suffers a malfunction.

Piston 30 is provided with means for triggering reversal of the piston stroke and also with means for damping the movement of the piston at the termination of each stroke.

For these purposes the piston 30 as shown in FIG. 2 is provided with an annular groove 54 of substantial width, an intermediate land 56, and'a second annular groove 58 of substantial width. The spacing of grooves 54, 58 is substantially equal to the length of the piston stroke.

Rearwardly from groove 58 there is present a stepped land consisting of an inner segment 60 and an outer segment 62. These create a shoulder 64 at their junction.

Cooperating with'piston 30 in reversing and damping the motion of the piston is a guide sleeve, indicated generally at 70.

Guide sleeve 70 slidably receives the piston 30. Its exterior surface is formed with a plurality of longitudinally spaced, annular grooves and associated ports which serve as passageways for the operating fluid.

At the forward end of the sleeve 70 there is present an annular groove 72 with associated port 74 which passes exhaust oil. Spaced rearwardly from groove 72 as shown in FIG. 2 are a first pair of annular grooves 76a, 76b with associated ports 78a, 78b and a second pair of annular grooves 80a, 80b with associated ports 82a, 82b. At timed intervals each pair overlies one of grooves 54, 58 on piston 30 and transmits fluid during consummation ofthe operation by which the direction of piston motion is reversed.

Rearwardly from the groove pairs above described are another pair of grooves 84, 86. These grooves 84, 86 also. are spaced from each other by a distance substantially equal to the piston stroke. Each communicates with the interior of the sleeve 70 through a check valve.

Groove .84 communicates with the interior of the sleeve through a check valve indicated generally at 87.

As indicated particularly in FIG. 3a, the check valve 87 comprises an annular, recess 88 located centrally of groove 84. A plurality of radially spaced perforations 9 0 communicate with the interior of the sleeve. Serrated retaining ridges 92 extend radially outwardly on each margin of recess 88.

An expandable valving member such as a rubber or plastic 'seal ring 94 is seated loosely in the recess. This ring 94 permits passage of fluid in one direction only through perforations 90, this establishing a check valve function.

A check valve indicated generally at 95 is associated with annular groove 86.

As shown in FIG. 3b, check valve 95 is analogous in its construction and function to check valve 87. Check valve 95 comprises an annular recess 96 which communicates with radially spaced perforations 98. Serrated retaining ridges 100 extend radially outwardly fromeach margin of the recess 96. A resiliently deformable rubber or plastic seal ring 102 is seated in the recess 96 over the perforations. Like ring 94, ring 102 serves as a check valve which permits passage of 'fluid in one direction only through the perforations 98.

v The inner surface of guide sleeve 70 has an annular shoulder 104 at its forward end. This cooperates with shoulder 64 on the rearward end of the piston 30 in defining a chamber 105. A cooperating chamber 107 lies behind the piston 30.

Guide sleeve 70 further provided with a small port 106 located at a predetermined location, in groove 84 in 'theillustration, and communicating with the interior of the sleeve 70.

A groove 108 is present at the rearward end of the sleeve 70. This retains a tube 140 by means of which fluid under pressure is supplied to chamber 52, as will appear hereinafter.

Cooperating with guide sleeve 70 in channeling operating fluid to the piston 30 is a channeled sleeve indicated generally at 110. Its construction is shown particularly in FIG. 9. I

The channeled sleeve 110 is dimensioned for a smooth, sliding fit over the guide sleeve and is of substantially the same length. It is provided with a first longitudinal, exterior channel 112 with associated port 114. This communicates with annulargroove 72 of the guide sleeve 70.

Channeled sleeve also has an external, longitudinally extending channel 1 15. This is provided at spaced intervals along its length with ports 116, 118, and 122.

Port 116 communicates with annular groove 78a in guide sleeve 70; port 118 with groove 82b; ports 120 with grooves 84; and ports 122 with groove 86.

Channeled sleeve 1 10 is provided with two additional longitudinally extending channels: Channel 124 having port 126 formed therein and channel 128 having port 130 formed therein. Port 126 communicates with annular groove 76b and port 130 with annular groove 80a of the guide sleeve 70.

Direct communication thus is provided from the area inside the guide sleeve 70 in which the piston 30 moves and with the channels 112, 115, 124 and 128 of channel'sleeve 110. The channels 112, 115, 124 and 128 in turn all open out at the rear of the sleeve 1 10 and communicate with the various components of the conduit system. In this system means is provided for connecting pressure fluid chamber 52 located to the rear of the back face 50 of the piston 30 with a source of fluid under pressure.

To this end there is supplied a tube 140, FIGS. 2, 3a and 3b. This has a'stem 142 dimensioned for sliding reception inside the bore of the piston 30 which defines chamber 52. The stem 142 is of sufficient length to be thus received during the entire piston stroke.

The tube has a flange 144 at its rearward end. The flange 144'is received in internal groove 108 of the guide sleeve 70 and has on its exterior face an annular groove 145 in which is seated a ring 146. Fluid under pressure thus may be delivered through the tube 140 directly to chamber 52, behind the piston 30 so-thatv rapid piston advancement may be'obtained. The stem 142 effectively reduces-the working quantity of fluid in chamber 52' required to advance the piston, whereby to increase the operating rate of the latter.

The conduit system also includes means for connecting the tamper with a source of fluid under pressure, e.g. an hydraulic pump.

As shown in FIG. 3b, the connecting conduit means comprise a pressure line connected to the pressure side of the pump and a low pressure return line 152 connected to the return side of the pump.

Interposed between the piston 30 and the source of fluid under pressure is valve means having for its function reversing the flow of fluid to the piston 30 at the end of'each piston stroke. The valve means employed is of a type which is actuated by the movement of the piston 30 itself.

In the illustrated form of the invention, a spool valve is used for the indicated purpose. Its construction is shown particularly in FIGS. 2, 3b and 4.

As noted above valve case 24 has a transverse bore which forms a chamber 28. The case 24 also has several passageways which connect with the various conduits comprising the fluid circuit.

Thus there is a first passageway 154 which communicates with pressure line 150 and a second passageway 156 which is coupled to return line 152.

On the opposite side of chamber 28 there are located a central passageway 158 which communicates with tube 140; a passageway 160 which communicates with channel 1 12 in channeled sleeve 110; passageways 162, 164 which communicate respectively with channels 128, 124 of the channeled sleeve 110; and a passageway 166 which communicates with channel 115 thereof.

Mounted within transverse bore 28 is a valve spool housing 170. This is retained in a stationary position by caps 172 and retaining rings 174, one pair at each end of the housing 170.

The spool housing 170 is formed with a longitudinal bore 176 which extends from end to end. Bore 176 is enlarged at spaced points along its length to provide chambers indicated particularly in FIG. 3b by numerals 178, 180, 182, 184 and 186. A connecting passageway 190 interconnects chambers 178 and 186.

An exterior channel 192 extends lengthwise of spool body 170, FIG. 4. It communicates at one of its ends with one end 176b of bore 176; at the other of its ends, with a sniall port 194 which leads into the central portion of bore 176.

A companion channel 196 is present on the opposite side of the spool housing 170. It communicates at one of its ends with the opposite end 176a of bore 176. A port 198 of small dimensions connects the inner end of channel 196 with tle central part of bore 176.

Spool housing 170 further is formed with a plurality of side ports which connect the inner chambers with the exterior, FIG. 3b. Two of these, 202, 204 connect, respectively, with channels 158, 160. Another pair 206, 208 connect, respectively, with passageway 154 coupled to the high pressure fluid line 150 and passageway 156 coupled tothe low pressure exhaust line 152.

A valve spool, indicated generally at 210 is mounted for reciprocating movement within bore 176 of the valve housing 170. The spool 210 includes in sequence a terminal land 212, a groove 214, a central land 216, a groove 2 l8 and a terminal land 220. In the operation of the valve, the spool 210-shifts alternately from one end of the housing 170 to the other, connecting the appropriate passageways through grooves 214, 218.

OPERATION The operation of the herein described fluid operated reciprocating motor 12 as applied to an earth tamper or related apparatus is as follows:

Fluid under pressure as best understood with reference to FIGS. 3b, 8 and 11 enters through conduit 150. It passes to piston 30 via passageway 154, port 206, chamber 182, chamber 180, port 202, passageway 158, tube 140, and thence into chamber 52 behind the back face 50 of the piston 30. The pressurized fluid not only applies pressure behind the piston 30, but also pressurizes both ends of spool 210-that the spool 210 remains stqabilized in its operative position. This is accomplished by fluid passing through ports 194, 198 in spool housing 170 and associated channels 192, 196 to both ends 176b and 176a, respectively, of the spool 210, establishing equal pressure and stabilizing the spool 210.

As the piston 30 advances, fluid as best understood with reference to FIGS. 30, 3b and 11 is pushed by the front face 48, 48a of the piston 30 out through port 114 into channel 1 12. This conducts the fluid back through passageway 160, port 204 of the valve housing 170, chambers 184, 186, port 208, passageway 156 and conduit 152, back to the low pressure exhaust line.

As noted above, it is a primary feature of the invention that the piston 30 itself actuates the valve to reverse the piston stroke. This is accomplished by means of annular grooves 54, 58 on the piston 30, grooves 76a and 76b and 80a and 80b of guide sleeve 70, and other associated fluid circuitry.

The principle involved is that of establishing a circuit interconnecting pressurized bore 176 on one end 176a or the other 176b of valve spool 210 with low pressure exhaust line 152 while maintaining high pressure at the other end 176b or 176a, respectively, of the spool 210. When one end of the bore 176 is thus vented to a low pressure area, the high pressure at the other end forces the spool 210 to move positively the length of the bore 176 so that a circuit is established which reverses the direction of stroke of the piston 30.

Thus, as is shown particularly in the fluid circuit diagram of FIG. 11 with the piston 30 positioned as illustrated in FIG. 3a, groove 58 of the piston 30 underlies groove pair 80a, 80b of guide sleeve 70 and communicates therewith through ports 82a, 82b. High pressure fluid from the upper end 176a of bore 176 thereupon passes though channel 196, passageway 162, channel 128, port 130, port 82a, port 82b. port 118, channel 115, passageway 166 and thus to low pressure conduit 152. At the same time, in view of the seal provided by lands 212, 220 of the valve spool 210 high pressure is maintained at the opposite end 176b of the valve spool 210.

This establishes a pressure differential between the two ends 176b and 176a of the valve spool 210 such that the high pressure at the lower end 176b of bore 176 forces the spool 210 accordingly to, shift to the position of FIG. 8. With the valve spool 210 so positioned, the motor 12 is conditioned for the return stroke of the piston 30.

In the return stroke, as best seen with reference to FIG. 8, high pressure fluid passes through conduit 150, passageway 154, port 206, chambers 182-and 184, port 204, passageway 160, in the valve body; and through channel 112 in channeled sleeve 110. It discharges as understood with reference to FIG. 3a through port 114 to the area ahead of the piston 30 where it impinges upon piston front face 48 to drive the piston 30 rearwardly.

At the same time, piston back face 50 as shown in FIGS. 3a and 8 is connected to the low pressure exhaust line. Fluid from chamber 52 behind the piston passes through tube 140, passageway 158, port 202, chamber 180, chamber 178, passageway 190, chamber 186, port 208, passageway 156 and thence to low pressure conduit 152.

When the piston 30 has reached its fully retracted position, groove 54 of the piston 30 as understood with reference to FIG. 12 underlies grooves 76a, 76b and as: sociated ports 78a and 78b of guide sleeve 70. This establishes a circuit via channel 1 15 of channeled sleeve and passageway 166, between bore 176 at the other end 176b of the spool housing and low pres sure line 152. The effect opposite to that above described then occurs.

That is, by virtue of the seal provided by lands 212, 220 of the valve spool 210, high pressure is maintained atthe opposite end 176a of the valve spool 210. This establishes a pressure differential between the two ends 176a and 176k of the valve spool 210 such that the high pressure at the upper end 176a of bore 176 forces the spool 210 accordingly to shift to the position of FIG. 3a thereby conditioning the motor 12 for the forward or drive stroke of the piston 30.

Movement of the piston 30 is arrested smoothly and positively at the end of each stroke through the action of a fluid circuit, shown in FlG. 13, including'check valves which exert a damping or choking effect. As has been noted, land segment 62 at the innermost end of the piston 30 is in sliding contact with the interior wall of guide sleeve 70. It thus creates two chambers: A small volume chamber 105 forwardly of the land 62 and a relatively large volume chamber 107 rearwardly of the land 62. Check valves 87, 95 interconnect these chambers 1 05, 107 with low pressure channel 115 in channeled sleeve 1 10. The check valves 87 and 95 are operative in the direction of restricting the flow of oil from low pressure channel 115 into the chambers 105 and 107 but permitting such flow in the reverse direction. Port 106 of small restricted cross section also interconnects the chambers 105, 107 with low pressure channel 115.

Since there is a sliding fit between the piston 30 and the sleeve 70, it is possible for a certain amount of oil to escape around the piston 30, and this also plays a part inthe damping action, by means of which the piston 30 is brought to a halt at the end of each stroke.

As the piston 30 reciprocates within the guide sleeve 70, it establishes a vacuum in chamber 107 on the forward stroke and in chambers 105 on the reverse stroke.

As soon as the vacuum isestablished, a limited amount of fluid is sucked into one orthe, other of the chambers 105,.107 through port l06froin low pressure channel 115. Thus in both directions of travel the piston 30 pushes ahead of it a certain amount of oil within one or the other of these two chambers 105, 107.

As the piston 30 moves forwardly to its fully advanced. positionof FIG. 3a, it establishes a vacuum in chamber 107.. Accordingly, as soon as land 62 sweeps past port 106, oil is sucked into the chamber 107 in restricted amount.

As the piston 30 advances, it pushes ahead of it oil which has been introduced into chamber 105 during the reverse piston stroke. Since the size of port 106 is very small, not enough oil is present in the chamber 105 to completely fill it. Accordingly the piston 30 moves rapidly through the first portion of its stroke.

However, as the piston 30 nears the terminal portion of its stroke, it starts working against the oil in the chamber 105, pushing it as understood with reference to FIG. 13 through check valve 87 into low pressure channel 115 and damping the forward motion of thepiston 30 in a first stage. A second stage of damping occurs after land 62 has passed check valve 87. When this occurs, a very small but significant amount of oil escapes around the piston 30 preventing the sudden shock which otherwise would occur if shoulder 64 of land 62 should come abruptly against a pocket of incompressible fluid.

contemporaneously with the damping of the piston 30, groove 58 thereof moves into operative position with guide sleeve grooves 80a, 80b and associated ports 82a, 82b. These establish the circuit which reverse the piston 30 as explained above.

During the reverse stroke of the piston a similar damping sequence occurs. Since chamber 107 behind the piston 30 is only partly filled with fluid, the piston 30 moves rapidly during the first part of its stroke. Toward the end of the piston stroke, the oil in chamber 107 completely fills the space ahead of the piston 30 so that the condition of FIG. 8 is reached. Thereafter, and until land 62 passes check valve 95, oil is displaced through the check, valve into low pressure channel 115. This accomplsihes the first stage damping of the piston 30. After the piston 30 has passed check valve 95, its motion is damped further and severely in a final damping stage which involves passage of a very small amount of fluid around the piston 30 itself. At the same time, registration occurs of groove 54 of the piston 30 with ports 78a, 78b of the guide sleeve 70, establishing the reversing circuit previously described.

As this constituted and operated, the fluid-operated motor l2'of the invention has significantadvantages. When used to drive an earth tamper by means of an hydraulic circuit established by the engine of a truck, the tamper may be operated at a low speed of a few hundred strokes per minute, as determined by the idle speed of the truck engine, or at a high speed of the order of 2,500 piston strokes per minute. The design easily may be altered to lengthen the piston stroke to several feet where this is necessary. Damage to the mechanism is prevented by the effective damping action occurring at the end of each stroke. It is impossible for the piston 30 to stop at dead center in an intermediate position. It always returns to the end of a stroke so that it is operational immediatelyupon actuation of the control valve. In addition, the circuit is applicable to a wide variety of reciprocating tools and thus provides a highly versatile and useful source of driving power.

Having thus. described the invention, I claim:

I. A fluid operating reciprocating motor comprising:

ii. said return conduit means interconnecting said piston with a fluid exhaust means;

iii. said valve means including a valving element connected in fluid flow relation with said high pressure conduit means between said piston and said source of high pressure fluid and in fluid flow relation with said return conduit means between said piston and said fluid exhaust means, said valving element being automatically shiftable between a first position and a second position, said valving element in said first position thereof directing a flow of high pressure fluid from said source of high pressure fluid against said first face of said piston to move said piston from said first position of said piston to said second position of said piston, and said valving element in said second position thereof directing the flow of high pressure fluid from said source of high pressure fluid against said second face of said piston to move said piston from said second position of said position to said first position of said piston;

iv. said valve shifting means creating a fluid pressure differential across said valving element at the completion of each reciprocation of said piston to alternately shift said valving element between said first position of said valving element and said second position of said valving element to thereby cause said piston to reciprocate between said first and second positions of said piston; and

d. damping means operable for damping the movement of said piston at the termination of a reciprocation thereof, said damping means comprising check valve means including a guide sleeve slidably receiving said piston, said guide sleeve cooperating with said piston to provide at least one chamber between said guide sleeve and said piston, means interconnecting said chamber in fluid flow relation with said return conduit means for periodically providing a flow of fluid from said return conduit means to said chamber, said guide sleeve having an annular groove formed therein and a plurality of openings of predetermined size formed therethrough interconnecting said annular groove with said chamber, and said check valve means further including a seal ring seated in said annular groove, said seal ring expanding in response to fluid pressure being applied thereto as said piston approaches the termination of a reciprocation to permit a controlled flow of fluid from said chamber through said plurality of openings to said annular groove thereby to cause damping of the movement of said piston.

2. A fluid operated reciprocating motor comprising:

a. a case for said motor; b. a piston mounted for reciprocation in said case between a first position and a second position, said piston having a front face, a back face, and a cylindrical bore extending inwardly from-said back face of said piston;

i. said back face of said piston comprising an end wall of said cylindrical bore;

ii. said cylindrical bore of said piston having a diameter substantially less than the overall diameter of said piston such that only a relatively small amount of fluid is required to fill said cylindrical bore to apply pressure against said back face to cause movement of said piston;

iii. said back face of said piston having a substantially greater area than said front face of said piston such that in the event the movement of said piston is interrupted at a point other than the termination of a reciprocation, the differential pressure of the fluid applied across said back face and said front face operates to cause said piston to move to said second position thereof;

0. a hydraulic circuit for reciprocating said piston,

said hydraulic circuit including high pressure conduit means, return conduit means, valve means, and valve shifting means;

i. said high pressure conduit means interconnecting said piston with a source of high pressure fluid;

ii. said return conduit means interconnecting said piston with a fluid exhaust means;

iii. said valve means including a valving element connected in fluid flow relation with said high pressure conduit means betewen said piston and said source of high pressure fluid and in fluid flow relation with said return conduit means between said piston and said fluid exhaust means, said valving element being alternately shiftable between a first position and a second position, said valving element in said first position thereof directs a flow of high pressure fluid from said source of high pressure fluid against said back face of saidpiston to move said piston from said first position of said piston to said second position of said piston, and said valving element in said second position thereof directing a flow of high pressure fluid from said source of high pressure fluid against said front face of said piston to move said piston from said second position of said piston to said first position of said piston;

iv. said valve shifting means creating a fluid pressure differential across said valving element at the completion of each reciprocation of said piston to alternately shift said valving element between said first position of said valving element and said second position of said valving element to thereby cause said piston to reciprocate between said first and second positions of said piston; and

d. damping means comprising check valve means operable for damping the movement of said piston at the termination of each reciprocation thereof.

3. A fluid operated reciprocating motor comprising:

a. a case for said motor;

b. a piston mounted for reciprocation in said case between a first position and a second position, said position having a front face and a back face;

c. a hydraulic circuit for reciprocating said piston,

said hydraulic circuit including high pressure conduit means, return conduit means, valve means, and valve shifting means;

i. said high pressure conduit means interconnecting said piston with a source of high pressure fluid;

ii. said return conduit means interconnecting said piston with a fluid exhaust means;

iii. said valve means including a valving element connected in fluid flow relation with said high pressure conduit means between said piston and said source of high pressure fluid and in fluid flow relation with said return conduit means between said piston and said fluid exhaust means, said valving element being alternately shiftable between a first position and a second position, said valving element in said first position thereof directing a flow of high pressure fluid from said source of high pressure fluid against said back face of said piston to move said piston from said first position of said piston to said second position of said piston, and said valving element in said second position thereof directing a flow of high pressure fluid from said source of high pressure fluid against said front face of said piston to move'said piston from said second position of said piston to said first position of said piston; iv. said valve shifting element creating a fluid pressure differential across said valving element at the completion of each reciprocation of said piston to alternately shift said valving element between said first position of said valving element and said second position of said valving element .to thereby cause said piston to reciprocate between said first and second positions of said piston; and d. resilient abutment means mounted in said case forward of said second position of said piston, said resilient abutment means including metallic contact means operable to cause the emission of a metallic sound in the event said piston travels past said second position thereof and strikes said metallic contact means as a result of a malfunction in said hydraulic circuit thereby providing an audible indication of the occurrence of said malfunction.

4. A fluid operated reciprocating motor comprising:

a. a case for said motor;

b. a piston mounted for reciprocation in said case between a first position and a second position, said piston having a front face and a back face;

0. high pressure conduit means interconnecting said piston with a source of high pressure fluid; return conduit means interconnecting said piston with a fluidexhaust means;

- d. pressure actuatable valve means including a valve housing, a spool valve, pressure equalizing conduit means, and valve shifting conduit means; i. said valve housing defining a valve chamber connectedin fluid flow relation with said high pressure conduit means between said piston and said source of high pressure fluid and in fluid flow relation with said return conduit means between said piston and said fluid exhaust means;

said spool valve being mounted in said valve chamber for movement between a first position wherein said spool valve directs a flow of high pressure fluid from said source of high pressure fluid against said backface of said piston to move said piston from said first position thereof to said second position thereof, and a second position wherein said spool valve directs a flow of high pressure fluid from said source of high pressure fluid against said front face of said piston' to move said piston from said second position thereof to said firstposition thereof;

iii. said pressure equalizing conduit means interconnecting said high pressure conduit means in fluid flow relationshipwith each end of said valve chamber such as to normally equalize the fluid pressure applied in said valve chamber against the ends of said spool valve; and

iv. said ,valve shifting conduit means including first conduit means operable for interconnecting one end of said valve chamber with said return conduit means during at least a portion of the movement of said piston form said first position thereof to said second position thereof such as to permit a flow of fluid from said one end of said valve chamber to said return conduit means thereby to establish a-pressure differential across the ends of said spool valve to cause said spool valve to shift from said first position thereof to said second position thereof as said piston completes its movement from said first position thereof to said second position, and said valve shifting conduit means further including a second conduit means operable for interconnecting the other end of said valve chamber with said return conduit means during at least a portion of the movement of said piston from said second position thereof to said first position thereof such as to permit a flow of fluid from said other end of said valve chamber to said return conduit means thereby to establish a pressure differential across the ends of said spool valve to cause said spool valve to shift from said second position thereof into said first position thereof as said piston completes its movement from said second position thereof to said first position thereof. 5. A fluid operated reciprocating motor as set forth in claim 4 wherein said piston further includes a cylindrical bore extending inwardly from said back face of I said piston, said back face of said piston comprises an end wall of said cylindrical bore, said-cylindrical bore of said piston has a diameter substantially less than the overall diameter of said piston such that only a relatively small amount of fluid is required to fill said cylindrical bore to apply pressure against said back face to cause movement of said piston and said back face of said piston has a substantially greater area than said front face of said piston such that in the event the movement of said piston is interrupted'at a point other than the termination of a reciprocation the differential pressure of the fluid applied across said back face and said front face operates to cause said piston to move to said second position thereof.

6. A fluid operated reciprocating motor as set forth in claim 4 further comprising resilient abutment means mounted in said case forward of said second position of said piston, said resilient abutment means including metallic contact means operable to cause the emission of a metallic sound in the event said piston travels past said second position thereof and strikes said metallic contact means as a result of a malfunction insaid hydraulic circuit thereby providing an audible indication of the occurrence of said malfunction.

7. A fluid operated reciprocating motor as set forth in claim 4 further comprises damping means operable for damping the movement of said piston at the termination of a reciprocation thereof in at least one direction, said damping means comprising check valve means including a guide sleeve slidably receiving said piston, said guide sleeve cooperating with said piston to provide at least a first chamber between said guide sleeve and said piston, said guide sleeve having at least a first annular groove formed therein and at least a first plurality of openings of predetennined size formed therethrough interconnecting said first annular groove with said first chamber, means interconnecting said first chamber in fluid flow relation with said return conduit means for periodically providing a flow of fluid from said return conduit means to said first chamber, and said check valve means further including a first seal ring seated in said first annular groove, said first seal ring expanding in response to fluid pressure being applied thereto as said piston approaches the termination of its reciprocation in said one direction to permit a controlled flow of fluid from said first chamber through said first plurality of openings to said first annular groove to cause a damping of the movement of said piston as said piston approaches the end of its movement in said one direction.

8. A fluid operated reciprocating motor as set forth in claim 7 wherein said guide sleeve of said check valve means cooperates with said piston to provide a second chamber between said guide sleeve and said piston, said guide sleeve has a second annular groove formed therein and second plurality of openings of predetermined size formed therethrough interconnecting said annular groove with said second chamber, said means interconnecting said first chamber in a fluid flow relation with said return conduit means also interconnects said second chamber in fluid flow relation with said return conduit means for periodically providing a flow of fluid from said return conduit means to said second chamber, and said check valve means further includes a second seal ring seated in said second annular groove, said second seal ring expanding in response to fluid pressure being applied thereto as said piston approaches the termination of its reciprocation in the opposite direction to permit a controlled flow of fluid from said second chamber to said second plurality of openings to said second annular groove thereby to cause a damping of the movement of said piston as said piston approaches the end of its movement in said opposite direction.

9. A fluid operated reciprocating motor as set forth in claim 8 wherein said means interconnecting said first and second chambers in a fluid flow relation with said return conduit means comprises a port formed at a predetermined location in said guide sleeve such that said port communicates with said first chamber to provide a flow of fluid thereto from said return conduit means during at least a portion of the movement of said piston in said opposite direction and communicates with said second chamber to provide a flow of fluid thereto from said return conduit means during at least a portion of the movement of said piston in said opposite direction.

10. A fluid operated reciprocating motor as set forth in claim 8 wherein said guide sleeve includes further means operable after said first seal ring has expanded to provide a second stage of damping as said piston approaches the termination of its movement in said one direction, and also operable after said second seal ring has expanded to provide a second stage of damping as said piston approaches the termination of its movement in said opposite direction.

11. In a fluid operated reciprocating motor having a piston mounted for reciprocation first in one direction and then in the opposite direction, and hydraulic circuit means for reciprocating said piston including a return conduit means interconnecting said piston with a fluid exhaust means, the combination therewith of damping means for damping the movement of said piston at the termination of a reciprocation thereof in at least one direction, said damping means comprising:

a. check valve means including a guide sleeve slidably receiving said piston;

i. said guide sleeve cooperating with said piston to provide at least a first chamber between said guide sleeve and said piston;

ii. said guide sleeve having at least a first annular groove formed therein and at least a first plurality of openings of predetermined size formed therethrough interconnecting said first annular groove with said first chamber;

b. means interconnecting said first chamber in fluid flow relation with said return conduit means for periodically providing a flow of fluid from said return conduit means to said first chamber; and

c. said check valve means further including a first seal ring seated in said first annular groove, said first seal ring expanding in response to fluid pressure being applied thereto as said piston terminates its reciprocation in said one direction to permit a controlled flow of fluid from said first chamber through said first plurality of openings to said first annular groove thereby to cause a damping of the movement of said piston as said piston approaches the end of its movement in said one direction.

12. In a fluid operated reciprocating motor as set forth in claim 11 wherein said guide sleeve of said check valve means cooperates with said piston to provide a second chamber between said guide sleeve and said piston, said guide sleeve has a second annular groove formed therein and a second plurality of openings of predetermined size formed therethrough interconnecting said annular groove with said second chamber, said means interconnecting said first chamber in fluid flow relation with said return conduit means also interconnects said second chamber in fluid flow relation with said return conduit means for periodically providing a flow of fluid from said return conduit means to said second chamber, and said check valve means further includes a second seal ring seated in said first annular groove, said second seal ring expanding in response to fluid pressure being applied thereto as said piston approaches the termination of its reciprocation in the opposite direction to permit a controlled flow of fluid from said second chamber through second plurality of openings to said second annular groove thereby to cause a damping of the movement of said piston as said piston approaches the end of its movement in said opposite direction.

13. In a fluid operated reciprocating motor as set forth in claim 12 wherein said means interconnecting said first and second chambers in fluid flow relation with said return conduit means comprises a port formed at a predetermined location in said guide sleeve such that said port communicates with said first chamber to provide a flow of fluid thereto from said return conduit means during at least a portion of the movement of said piston in said opposite direction and communicates with said second chamber to provide a flow of fluid thereto from said return conduit means during at least a portion of the movement of said piston in said one direction.

14. In a fluid operated reciprocating motor as set forth in claim 12 wherein said guide sleeve includes further means operable after said first seal ring has expanded to provide a second stage of damping as said piston approaches the termination of its movement in said one direction, and also operable after said second seal ring has expanded to provide a second stage of damping as said piston approaches the termination of its movement in said opposite direction.

15. In a fluid operated reciprocating motor having a piston mounted for reciprocation between a first position and a second position, high pressure conduit means connecting said piston to a source of high pressure fluid, and a return conduit means connecting said piston to fluid exhaust means, the combination thereof of pressure actuatable valve means for reciprocating said piston, said pressure actuatable valve means comprising:

a. a valve housing defining a valve chamber connected in fluid flow relation with said high pressure conduit means between said piston and said source of high pressure fluid and in fluid flow relation with said return conduit means between said piston and said fluid exhaust means;

b. a spool valve mounted in said valve chamber for movement between a first position wherein said spool valve directs a flow of high pressure fluid from said source of high pressure fluid against said piston to cause said piston to movefrom said first position thereof to said second position thereof, and a second position wherein said spool valve directs flow of high pressure fluid from said source of high pressure fluid against said piston to cause said piston tomove from said second position thereof to said first position thereof;

0. pressure equalizing conduit means interconnecting said high pressure conduit means in fluid flow relation with each end of said valve chamber such as to normally equalize the fluid pressure applied in said valve chamber against the ends of said spool valve; and i d. valve shifting conduit means including first conduit means operable for interconnecting one end of said valve chamber with said return conduit means during at least a portion of the movement of said piston from saidfirst position thereof to said second position thereof such as to permit a flow of fluid from said one end of said valve chamber to said return conduit means thereby to establish a pressure differential across the ends of said spool valve to cause said spool valve to shift from said first position thereof to said second position thereof as said piston completes its movement from said first position thereof to said second position thereof, and said valve shifting conduit means further including second conduit means operable for interconnecting the other end of said valve chamber with said return conduit means during at least a portion of the movement of said piston from said second position thereof to said first position thereof such as to permit a flow of fluid from said other end of said valve chamber to said return conduit means thereby to establish a pressure differential across the ends of said spool valve to cause said spool valve to shift from said second position thereof to said first position thereof as said piston completes its movement from said second position thereof to said first position thereof.

16. A fluid operated reciprocating motor comprising:

a. housing means for said motor, said housing means comprising a two-part structure including a case comprising the external housing for said motor and sleeve means supported within said case in juxtaposed relation to the innersurface of said case;

i. said sleeve means having at least one channel formed therein and at least one port formed therethrough interconnecting said channel with the interior of said sleeve means;

b. a piston mounted within said sleeve means for movement relative thereto between a first position and a second position, said piston including a first face and a second face;

0. high pressure conduit means interconnecting said piston with a source of high pressure fluid;

d. return conduit means interconnecting said piston with a fluid exhaust means;

e. valve means connected in fluid flow relation with said high pressure conduit means between said piston and said source of high pressure fluid and in fluid flow relation with said return conduit means between said piston and said fluid exhaust means,-

said valve means including a valving element alternately shiftable between a first position and a second position, said valving element in said first position thereof directing a flow of high pressure fluid against said first face of said piston and permitting a flow of fluid from said second face of said piston through said port to said channel in said sleeve means and therefrom to said return conduit means thereby causing said piston to move from said first position thereof to said second position thereof, and said valving element in said second position thereof directing a flow of high pressure fluid along said channel of said sleeve means to said port and therethrough against said second face of said piston and permitting a flow of fluid from said first face of said piston to said return conduit means thereby causing said piston to move from said second position thereof to said first position thereof; and valve shifting means operable to interconnect the opposite ends of said valving element to said return conduit means so as to provide a flow of fluid alternately from each end of said valving element to said return conduit means thereby to establish a pressure differential across the ends of said valving element at the completion of each reciprocation of said piston to alternately shift said valving element between said first position and said second position thereof to thereby cause said piston to reciprocate between said first and second positions thereof.

UNETED STALTES PATENT UFFICE CERTIWQATE 0F CORREflTlON Patent No. 80,0. 662 Dated April 2, 1974 It is certified that error appears in the above--identified patent and that said Letters Patent are hereby corrected as shown below:

Column 11, line 5, position" (second instance) should be piston;

Column 12, line 8, "betewen" should be between;

Column 12, line 42, "position" should be piston--;

Column 13, line 64, "form" should be ---f1rorn-.

Signed and sealed this 1st day of October 1974 (SEAL) Attest:

MCCOY M. GIBSON JR. C. MARSHALL DANN Attesting Officer Commissioner of Patents FORM FIG-1050 (10-69) uscoMM-oc 60376-P69 

1. A fluid operating reciprocating motor comprising: a. a case for said motor; b. a piston mounted for reciprocation in said case between a first position and a second position, said piston having a first face and a second face; c. a hydraulic circuit for reciprocating said piston, said hydraulic circuit including high pressure conduit means, return conduit means, valve means, and valve shifting means; i. said high pressure conduit means interconnecting said piston with a source of high pressure fluid; ii. said return conduit means interconnecting said piston with a fluid exhaust means; iii. said valve means including a valving element connected in fluid flow relation with said high pressure conduit means between said piston and said source of high pressure fluid and in fluid flow relation with said return conduit means between said piston and said fluid exhaust means, said valving element being automatically shiftable between a first position and a second position, said valving element in said first position thereof directing a flow of high pressure fluid from said source of high pressure fluid against said first face of said piston to move said piston from said first position of said piston to said second position of said piston, and said valving element in said second position thereof directing the flow of high pressure fluid from said source of high pressure fluid against said second face of said piston to move said piston from said second position of said position to said first position of said piston; iv. said valve shifting means creating a fluid pressure differential across said valving element at the completion of each reciprocation of said piston to alternately shift said valving element between said first position of said valving element and said second position of saId valving element to thereby cause said piston to reciprocate between said first and second positions of said piston; and d. damping means operable for damping the movement of said piston at the termination of a reciprocation thereof, said damping means comprising check valve means including a guide sleeve slidably receiving said piston, said guide sleeve cooperating with said piston to provide at least one chamber between said guide sleeve and said piston, means interconnecting said chamber in fluid flow relation with said return conduit means for periodically providing a flow of fluid from said return conduit means to said chamber, said guide sleeve having an annular groove formed therein and a plurality of openings of predetermined size formed therethrough interconnecting said annular groove with said chamber, and said check valve means further including a seal ring seated in said annular groove, said seal ring expanding in response to fluid pressure being applied thereto as said piston approaches the termination of a reciprocation to permit a controlled flow of fluid from said chamber through said plurality of openings to said annular groove thereby to cause damping of the movement of said piston.
 2. A fluid operated reciprocating motor comprising: a. a case for said motor; b. a piston mounted for reciprocation in said case between a first position and a second position, said piston having a front face, a back face, and a cylindrical bore extending inwardly from said back face of said piston; i. said back face of said piston comprising an end wall of said cylindrical bore; ii. said cylindrical bore of said piston having a diameter substantially less than the overall diameter of said piston such that only a relatively small amount of fluid is required to fill said cylindrical bore to apply pressure against said back face to cause movement of said piston; iii. said back face of said piston having a substantially greater area than said front face of said piston such that in the event the movement of said piston is interrupted at a point other than the termination of a reciprocation, the differential pressure of the fluid applied across said back face and said front face operates to cause said piston to move to said second position thereof; c. a hydraulic circuit for reciprocating said piston, said hydraulic circuit including high pressure conduit means, return conduit means, valve means, and valve shifting means; i. said high pressure conduit means interconnecting said piston with a source of high pressure fluid; ii. said return conduit means interconnecting said piston with a fluid exhaust means; iii. said valve means including a valving element connected in fluid flow relation with said high pressure conduit means betewen said piston and said source of high pressure fluid and in fluid flow relation with said return conduit means between said piston and said fluid exhaust means, said valving element being alternately shiftable between a first position and a second position, said valving element in said first position thereof directs a flow of high pressure fluid from said source of high pressure fluid against said back face of said piston to move said piston from said first position of said piston to said second position of said piston, and said valving element in said second position thereof directing a flow of high pressure fluid from said source of high pressure fluid against said front face of said piston to move said piston from said second position of said piston to said first position of said piston; iv. said valve shifting means creating a fluid pressure differential across said valving element at the completion of each reciprocation of said piston to alternately shift said valving element between said first position of said valving element and said second position of said valving element to thereby cause said piston to reciprocate between said first and second positions of said piston; and d. damping means cOmprising check valve means operable for damping the movement of said piston at the termination of each reciprocation thereof.
 3. A fluid operated reciprocating motor comprising: a. a case for said motor; b. a piston mounted for reciprocation in said case between a first position and a second position, said position having a front face and a back face; c. a hydraulic circuit for reciprocating said piston, said hydraulic circuit including high pressure conduit means, return conduit means, valve means, and valve shifting means; i. said high pressure conduit means interconnecting said piston with a source of high pressure fluid; ii. said return conduit means interconnecting said piston with a fluid exhaust means; iii. said valve means including a valving element connected in fluid flow relation with said high pressure conduit means between said piston and said source of high pressure fluid and in fluid flow relation with said return conduit means between said piston and said fluid exhaust means, said valving element being alternately shiftable between a first position and a second position, said valving element in said first position thereof directing a flow of high pressure fluid from said source of high pressure fluid against said back face of said piston to move said piston from said first position of said piston to said second position of said piston, and said valving element in said second position thereof directing a flow of high pressure fluid from said source of high pressure fluid against said front face of said piston to move said piston from said second position of said piston to said first position of said piston; iv. said valve shifting element creating a fluid pressure differential across said valving element at the completion of each reciprocation of said piston to alternately shift said valving element between said first position of said valving element and said second position of said valving element to thereby cause said piston to reciprocate between said first and second positions of said piston; and d. resilient abutment means mounted in said case forward of said second position of said piston, said resilient abutment means including metallic contact means operable to cause the emission of a metallic sound in the event said piston travels past said second position thereof and strikes said metallic contact means as a result of a malfunction in said hydraulic circuit thereby providing an audible indication of the occurrence of said malfunction.
 4. A fluid operated reciprocating motor comprising: a. a case for said motor; b. a piston mounted for reciprocation in said case between a first position and a second position, said piston having a front face and a back face; c. high pressure conduit means interconnecting said piston with a source of high pressure fluid; return conduit means interconnecting said piston with a fluid exhaust means; d. pressure actuatable valve means including a valve housing, a spool valve, pressure equalizing conduit means, and valve shifting conduit means; i. said valve housing defining a valve chamber connected in fluid flow relation with said high pressure conduit means between said piston and said source of high pressure fluid and in fluid flow relation with said return conduit means between said piston and said fluid exhaust means; ii. said spool valve being mounted in said valve chamber for movement between a first position wherein said spool valve directs a flow of high pressure fluid from said source of high pressure fluid against said back face of said piston to move said piston from said first position thereof to said second position thereof, and a second position wherein said spool valve directs a flow of high pressure fluid from said source of high pressure fluid against said front face of said piston to move said piston from said second position thereof to said first position thereof; iii. said pressure equalizing conduit means intErconnecting said high pressure conduit means in fluid flow relationship with each end of said valve chamber such as to normally equalize the fluid pressure applied in said valve chamber against the ends of said spool valve; and iv. said valve shifting conduit means including first conduit means operable for interconnecting one end of said valve chamber with said return conduit means during at least a portion of the movement of said piston form said first position thereof to said second position thereof such as to permit a flow of fluid from said one end of said valve chamber to said return conduit means thereby to establish a pressure differential across the ends of said spool valve to cause said spool valve to shift from said first position thereof to said second position thereof as said piston completes its movement from said first position thereof to said second position, and said valve shifting conduit means further including a second conduit means operable for interconnecting the other end of said valve chamber with said return conduit means during at least a portion of the movement of said piston from said second position thereof to said first position thereof such as to permit a flow of fluid from said other end of said valve chamber to said return conduit means thereby to establish a pressure differential across the ends of said spool valve to cause said spool valve to shift from said second position thereof into said first position thereof as said piston completes its movement from said second position thereof to said first position thereof.
 5. A fluid operated reciprocating motor as set forth in claim 4 wherein said piston further includes a cylindrical bore extending inwardly from said back face of said piston, said back face of said piston comprises an end wall of said cylindrical bore, said cylindrical bore of said piston has a diameter substantially less than the overall diameter of said piston such that only a relatively small amount of fluid is required to fill said cylindrical bore to apply pressure against said back face to cause movement of said piston and said back face of said piston has a substantially greater area than said front face of said piston such that in the event the movement of said piston is interrupted at a point other than the termination of a reciprocation the differential pressure of the fluid applied across said back face and said front face operates to cause said piston to move to said second position thereof.
 6. A fluid operated reciprocating motor as set forth in claim 4 further comprising resilient abutment means mounted in said case forward of said second position of said piston, said resilient abutment means including metallic contact means operable to cause the emission of a metallic sound in the event said piston travels past said second position thereof and strikes said metallic contact means as a result of a malfunction in said hydraulic circuit thereby providing an audible indication of the occurrence of said malfunction.
 7. A fluid operated reciprocating motor as set forth in claim 4 further comprises damping means operable for damping the movement of said piston at the termination of a reciprocation thereof in at least one direction, said damping means comprising check valve means including a guide sleeve slidably receiving said piston, said guide sleeve cooperating with said piston to provide at least a first chamber between said guide sleeve and said piston, said guide sleeve having at least a first annular groove formed therein and at least a first plurality of openings of predetermined size formed therethrough interconnecting said first annular groove with said first chamber, means interconnecting said first chamber in fluid flow relation with said return conduit means for periodically providing a flow of fluid from said return conduit means to said first chamber, and said check valve means further including a first seal ring seated in said first annular groove, said first seal ring expanding in response To fluid pressure being applied thereto as said piston approaches the termination of its reciprocation in said one direction to permit a controlled flow of fluid from said first chamber through said first plurality of openings to said first annular groove to cause a damping of the movement of said piston as said piston approaches the end of its movement in said one direction.
 8. A fluid operated reciprocating motor as set forth in claim 7 wherein said guide sleeve of said check valve means cooperates with said piston to provide a second chamber between said guide sleeve and said piston, said guide sleeve has a second annular groove formed therein and second plurality of openings of predetermined size formed therethrough interconnecting said annular groove with said second chamber, said means interconnecting said first chamber in a fluid flow relation with said return conduit means also interconnects said second chamber in fluid flow relation with said return conduit means for periodically providing a flow of fluid from said return conduit means to said second chamber, and said check valve means further includes a second seal ring seated in said second annular groove, said second seal ring expanding in response to fluid pressure being applied thereto as said piston approaches the termination of its reciprocation in the opposite direction to permit a controlled flow of fluid from said second chamber to said second plurality of openings to said second annular groove thereby to cause a damping of the movement of said piston as said piston approaches the end of its movement in said opposite direction.
 9. A fluid operated reciprocating motor as set forth in claim 8 wherein said means interconnecting said first and second chambers in a fluid flow relation with said return conduit means comprises a port formed at a predetermined location in said guide sleeve such that said port communicates with said first chamber to provide a flow of fluid thereto from said return conduit means during at least a portion of the movement of said piston in said opposite direction and communicates with said second chamber to provide a flow of fluid thereto from said return conduit means during at least a portion of the movement of said piston in said opposite direction.
 10. A fluid operated reciprocating motor as set forth in claim 8 wherein said guide sleeve includes further means operable after said first seal ring has expanded to provide a second stage of damping as said piston approaches the termination of its movement in said one direction, and also operable after said second seal ring has expanded to provide a second stage of damping as said piston approaches the termination of its movement in said opposite direction.
 11. In a fluid operated reciprocating motor having a piston mounted for reciprocation first in one direction and then in the opposite direction, and hydraulic circuit means for reciprocating said piston including a return conduit means interconnecting said piston with a fluid exhaust means, the combination therewith of damping means for damping the movement of said piston at the termination of a reciprocation thereof in at least one direction, said damping means comprising: a. check valve means including a guide sleeve slidably receiving said piston; i. said guide sleeve cooperating with said piston to provide at least a first chamber between said guide sleeve and said piston; ii. said guide sleeve having at least a first annular groove formed therein and at least a first plurality of openings of predetermined size formed therethrough interconnecting said first annular groove with said first chamber; b. means interconnecting said first chamber in fluid flow relation with said return conduit means for periodically providing a flow of fluid from said return conduit means to said first chamber; and c. said check valve means further including a first seal ring seated in said first annular groove, said first seal ring expanding in response to fluid prEssure being applied thereto as said piston terminates its reciprocation in said one direction to permit a controlled flow of fluid from said first chamber through said first plurality of openings to said first annular groove thereby to cause a damping of the movement of said piston as said piston approaches the end of its movement in said one direction.
 12. In a fluid operated reciprocating motor as set forth in claim 11 wherein said guide sleeve of said check valve means cooperates with said piston to provide a second chamber between said guide sleeve and said piston, said guide sleeve has a second annular groove formed therein and a second plurality of openings of predetermined size formed therethrough interconnecting said annular groove with said second chamber, said means interconnecting said first chamber in fluid flow relation with said return conduit means also interconnects said second chamber in fluid flow relation with said return conduit means for periodically providing a flow of fluid from said return conduit means to said second chamber, and said check valve means further includes a second seal ring seated in said first annular groove, said second seal ring expanding in response to fluid pressure being applied thereto as said piston approaches the termination of its reciprocation in the opposite direction to permit a controlled flow of fluid from said second chamber through second plurality of openings to said second annular groove thereby to cause a damping of the movement of said piston as said piston approaches the end of its movement in said opposite direction.
 13. In a fluid operated reciprocating motor as set forth in claim 12 wherein said means interconnecting said first and second chambers in fluid flow relation with said return conduit means comprises a port formed at a predetermined location in said guide sleeve such that said port communicates with said first chamber to provide a flow of fluid thereto from said return conduit means during at least a portion of the movement of said piston in said opposite direction and communicates with said second chamber to provide a flow of fluid thereto from said return conduit means during at least a portion of the movement of said piston in said one direction.
 14. In a fluid operated reciprocating motor as set forth in claim 12 wherein said guide sleeve includes further means operable after said first seal ring has expanded to provide a second stage of damping as said piston approaches the termination of its movement in said one direction, and also operable after said second seal ring has expanded to provide a second stage of damping as said piston approaches the termination of its movement in said opposite direction.
 15. In a fluid operated reciprocating motor having a piston mounted for reciprocation between a first position and a second position, high pressure conduit means connecting said piston to a source of high pressure fluid, and a return conduit means connecting said piston to fluid exhaust means, the combination thereof of pressure actuatable valve means for reciprocating said piston, said pressure actuatable valve means comprising: a. a valve housing defining a valve chamber connected in fluid flow relation with said high pressure conduit means between said piston and said source of high pressure fluid and in fluid flow relation with said return conduit means between said piston and said fluid exhaust means; b. a spool valve mounted in said valve chamber for movement between a first position wherein said spool valve directs a flow of high pressure fluid from said source of high pressure fluid against said piston to cause said piston to move from said first position thereof to said second position thereof, and a second position wherein said spool valve directs flow of high pressure fluid from said source of high pressure fluid against said piston to cause said piston to move from said second position thereof to said first position thereof; c. pressure equalizing conduit meanS interconnecting said high pressure conduit means in fluid flow relation with each end of said valve chamber such as to normally equalize the fluid pressure applied in said valve chamber against the ends of said spool valve; and d. valve shifting conduit means including first conduit means operable for interconnecting one end of said valve chamber with said return conduit means during at least a portion of the movement of said piston from said first position thereof to said second position thereof such as to permit a flow of fluid from said one end of said valve chamber to said return conduit means thereby to establish a pressure differential across the ends of said spool valve to cause said spool valve to shift from said first position thereof to said second position thereof as said piston completes its movement from said first position thereof to said second position thereof, and said valve shifting conduit means further including second conduit means operable for interconnecting the other end of said valve chamber with said return conduit means during at least a portion of the movement of said piston from said second position thereof to said first position thereof such as to permit a flow of fluid from said other end of said valve chamber to said return conduit means thereby to establish a pressure differential across the ends of said spool valve to cause said spool valve to shift from said second position thereof to said first position thereof as said piston completes its movement from said second position thereof to said first position thereof.
 16. A fluid operated reciprocating motor comprising: a. housing means for said motor, said housing means comprising a two-part structure including a case comprising the external housing for said motor and sleeve means supported within said case in juxtaposed relation to the inner surface of said case; i. said sleeve means having at least one channel formed therein and at least one port formed therethrough interconnecting said channel with the interior of said sleeve means; b. a piston mounted within said sleeve means for movement relative thereto between a first position and a second position, said piston including a first face and a second face; c. high pressure conduit means interconnecting said piston with a source of high pressure fluid; d. return conduit means interconnecting said piston with a fluid exhaust means; e. valve means connected in fluid flow relation with said high pressure conduit means between said piston and said source of high pressure fluid and in fluid flow relation with said return conduit means between said piston and said fluid exhaust means, said valve means including a valving element alternately shiftable between a first position and a second position, said valving element in said first position thereof directing a flow of high pressure fluid against said first face of said piston and permitting a flow of fluid from said second face of said piston through said port to said channel in said sleeve means and therefrom to said return conduit means thereby causing said piston to move from said first position thereof to said second position thereof, and said valving element in said second position thereof directing a flow of high pressure fluid along said channel of said sleeve means to said port and therethrough against said second face of said piston and permitting a flow of fluid from said first face of said piston to said return conduit means thereby causing said piston to move from said second position thereof to said first position thereof; and valve shifting means operable to interconnect the opposite ends of said valving element to said return conduit means so as to provide a flow of fluid alternately from each end of said valving element to said return conduit means thereby to establish a pressure differential across the ends of said valving element at the completion of each reciprocation of said piston to alternately shift said valving element between said fiRst position and said second position thereof to thereby cause said piston to reciprocate between said first and second positions thereof. 